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src/budget.ts holds the monthly budget model:

• createBudget(limits) builds category limits from the settings file.
• applyTransaction(budget, tx) subtracts spending and flags categories that go over.
• summarize(budget) returns the totals the dashboard shows.

It does no I/O itself; src/storage.ts loads and saves it.

Here's a plan for CSV export on the transactions page:

1. Add src/export/csv.ts with toCsv(rows, columns): quote every field, double embedded quotes, and use \r\n line endings so Excel opens it cleanly.
2. Add an Export CSV button to TransactionsPage that exports the currently filtered rows.
3. Name the file transactions-YYYY-MM-DD.csv.

export function toCsv(rows: Transaction[], columns: Column[]): string {  const escape = (value: string) => `"${value.replaceAll('"', '""')}"`;  const header = columns.map((c) => escape(c.label)).join(',');  const lines = rows.map((row) => columns.map((c) => escape(c.format(row))).join(','));  return [header, ...lines].join('\r\n');}

I've asked Codex to check the edge cases before we build it.

Mostly solid. Three things before building:

1. Formula injection. Payee names that start with =, +, - or @ are evaluated by Excel. Prefix those fields with '.
2. Encoding. Excel on Windows assumes the system code page, so non-ASCII payees turn into mojibake. Write a UTF-8 BOM (\uFEFF) first.
3. Size. Export only the filtered rows. This implementation builds the CSV in memory; test its memory use with large exports before deciding whether it needs streaming.

With those three, the plan is good to build.

Codex's three points are in the plan now. Ready to build when you are.

Done. Added src/export/csv.ts with escapeField and toCsv, wired an Export CSV button into TransactionsPage, and added two tests. The export includes only the filtered rows.